HDPE, as long as its the regular one without additives such as flame retardants, anti microbial, should be inert. I have had the followings in my tank with NO issues... HDPE, LDPE, PP, PVDF and ECTFE. My issue with PE/PP is that they float.
Great! Can you look at the White Starboard from King Plastics and give me your opinions on that one. This is the one I used below:
https://www.boatoutfitters.com/cut-to-size-white-white-king-starboard
